Arylamine N-acetyltransferases (NATs) catalyze the acetylation of extracyclic amino groups of aromatic amine and hydrazines. Two genes, NAT 1 or NAT 2, each exhibit polymorphisms that result in variation in NAT activities. Associations between acetylator phenotype and susceptibility to aromatic amine toxicity are well-known in adults. Little has been reported on contributions of NAT to developmental toxicity. The overall goal of the study is to investigate the role of NAT genotypes in aromatic amine-induced developmental genotoxicity. The hypothesis is that elevated NAT activities will increase the risk of aromatic amine induced developmental genotoxicity. The specific aims to test this hypothesis are: 1) to determine if maternal expression of NAT genes changes during pregnancy; 2) to investigate NAT 1 and NAT 2 pre- and post-natally; and 3) to correlate NAT 2 genotype with embryonic/fetal toxicity of 4-aminobiphenyl (4-AB) or 2- aminofluorene (2-AF). C57Bl/6 mice are classified as rapid acetylators and will be used as the model for aims 1 and 2. NAT 1 and NAT 2 mRNAs will be assessed by RT-PCR in non-pregnant and pregnant females and embryos or neonates. The presence of functional NAT proteins will also be evaluated by measuring acetylation of substrates of both isoforms, as well as those selective and/or specific for NAT 1 or NAT 2. For aim 3, C57Bl/6 mice and the congenic strain B6.A will be used. These strains have the same NAT 1 but differ in NAT 2 alleles resulting in high (C57Bl/6) and low (B6.A) levels of NAT activity. Pregnant animals will be exposed to the carcinogen, 4-AB or 2-AF and DNA adducts in the conceptus determined with specific antibodies. The four possible combinations of maternal and embryonic genotypes will be tested. In order to separate the contribution of maternal and embryonic genotypes, embryos of the high activity strain will be transferred to the low activity strain and vice versa. The results of these studies will show whether inter-individual variation in NAT 2 is associated with developmental genotoxicity. Such information would be useful in understanding potential human risk pregnancy and development, by identifying susceptible genotypes.